Widefield Triple Imaging Rig

[Gina]

With a triple imaging rig you don't need the optics to be apochromatic as each imager is only going to cover a narrow bandwidth.  We are talking about narrow band for widefield imaging as apart from M31, DSO imaging will be pretty much all nebulae and suchlike.

A combination of Asahi Pentax SMC real glass lenses and Atik 460EX can give great results.  Now that I have a decent 3D printer working I can readily produce the mechanics for remote focus, image alignment and so on.  I was struggling with ali plate, drills and files

[Gina]

I would like to thank Huw for resurecting this thread and for Earl and Paul's replies - it has encouraged me to look at this again and I am definitely going to persue it.  ATM I'm finding it hard to stick with any one project for very long so theis gives me another option

[Gina]

I have two options for using a widefield rig.  I was going to use the second pier but as the main one is a going concern, I could always take the MN190 and Esprit off the EQ8 and put the widefield rig on it.

Looking through this thread I see the wifefield rig hardly got a look-in.  By the time it was usable, the weather broke

I don't know when the second pier will be ready - I have yet to design the cover and work out power arrangements etc.

[Davey-T]

Good to see you're keeping busy Gina  don't want you getting bored   .

Don't forget I've got a 200mm SMC Takumar gathering dust somewhere which you are welcome to.

Dave

[Gina]

Good to see you're keeping busy Gina  don't want you getting bored   .

Don't forget I've got a 200mm SMC Takumar gathering dust somewhere which you are welcome to.

Dave

Thank you Dave   Especially for the offer   I would indeed like another 200mm SMC Takumar if you can find it.  Please let me know how much you want for it

Yes, I am mostly keeping busy though there are times when I don't feel like doing anything - fortunately not too many.

[Horwig]

I would like to thank Huw for resurecting this thread and for Earl and Paul's replies - it has encouraged me to look at this again and I am definitely going to persue it.  ATM I'm finding it hard to stick with any one project for very long so theis gives me another option

Glad to be of service, can't do with the busiest ATMer on the planet with not enough projects to think about

H

[Gina]

As I recall, I had some problems with the focussing - the timing belts tended to pull the lens sideways ever so slightly but enough to upset the image alignment.  I have alternative ideas to using timing belts and which can be printed in plastic.

Another problem with timing belts was changing lenses - the belt lengths and/or stepper positions would need changing.  Now what I want to do is arrange that different focal length lenses can be used with minimal fuss.

A big difference between telescopes and camera lenses is that the amount of movement of the focus control is far less with lenses.  We are talking of a range of maybe 10 degrees and a required accuracy around a tenth of a degree.

[Horwig]

I have a pentax 67 300mm ed lens I use for widefields, I use a timing belt for focus, and yes, the cfz is tiny, but using a stepper with a small pulley, and microstepping does the trick.

I've been playing with the idea of using multiple lenses to give faster imaging, the short gaps in the weather here mean that I never seem to complete any image.

Pentax lenses are very reasonable compared to 'name' telescopes, so multiple combinations of lenses will not break the bank. However, multiple cameras and filter wheels will.

Huw

[Gina]

I need two more 460EX cameras at a couple of hundred pounds under two grand each   Selling my two 314L+ cameras is unlikely to pay for even one of them

I was considering buying one of the new Lunt 50 solar scopes when they become available but I'm not sure now which I want most   I think I might leave getting an Ha solar scope until I've had a chance to look through one of someone else's and see if solar flares and prominences are as spectacular as some people think.  I very soon tired of white solar imaging - I'm afraid I didn't find sunspots very exciting.

What really interests me is doing something different from the run-of-the-mill and I think a widefield rig with 3 good cameras and fast lenses could be in this category

Another way-out project is the mono modified and cooled DSLR with built-in filter wheel.  This will go well with either the MN190 or Esprit 80ED.   And although providing an even wider FOV than the 460EX and lenses, using a FW really requires an APO optical system (or at least auto focussing when changing filters).  Three mono-fied DSLRs with individual NB filters and camera lenses would be interesting though   That is not impossible for sometime in the future but a modified DSLR is never going to come anywhere near a good quality astro CCD camera.  Just an interesting project I think.

[Gina]

I've been looking at my triple imaging rig and the problem areas.  I think I can continue to use the two different cameras with the corresponding different focal length lenses to cover a simailar FOV until I can release funds for another 460EX or two.

The main problem was the alignment of lens with camera - my engineering skills with the tools I had then were not good enough for the way I was doing it and the lenses were not well enough aligned with their respective cameras.  I'm now looking at a totally different arrangement with each imaging system as an entity with the filters slotting in rather than being mounted on a bar. 

Each imager will consist of lens screwed into an adapter ring.  Then a tube with a slot for the filter as in a filter drawer but a bit more compact, followed by a T2 mount for the camera.  I think I shall try a printed plastic construction initially but if it turns out that the plastic isn't rigid enough I can turn the parts in the lathe out of aluminium and finish with black anodising.  Even if it turns out that plastic is not suitable, at least I can get all the geometry sorted out before production in aluminium.

[Gina]

I have decided that I'm definitely going to buy another Atik 460EX mono CCD camera just as soon as I can arrange the funds.  The third will have to wait   With two 460EXs and one 314L+ I can use two 200mm lenses and one 135mm for instance and have best definition for Ha and OIII.  That will give me all I need for the "natural" palette and a good way towards the best Hubble palette.  I shall be looking carefully at what I want to keep of my astro gear and sell off a few things.

[Gina]

I'm now looking at the design of the lens, filter and camera connection unit.  There is a big difference between the dimensions of lenses of different focal lengths and the position of the focus sleeve.  This makes a common focus control difficult.  The longer lenses such as the 200mm put significant stress on the thread mount if this takes all the weight.  The 200mm SMC Takumar is quite heavy (640g).  So the longer lenses will have additional support.

The new design will differ from the previous one in several respects :-

1. Longer lenses will have additional support (not just the standard Pentax thread mount)
2. The method of driving the focus sleeve from a stepper motor will be different
3. The filters will be individually mounted rather than in one long bar
4. The guide camera and lens may be in a different place (not decided yet)

With the differences in the lenses I'm thinking of building individual housings and focus mechanisms.  I might even include a stepper motor in each individual housing - these stepper motors are very cheap.

Here is a photo showing the difference between the SMC Takumar 200mm and 105mm lenses.  The 55mm lens is even shorter than the 105mm etc.

[Gina]

Some calculations :-

Back focus of these lenses = 45mm

Back focus of Atik cameras = 13.5mm

Filter thickness = 3mm so correction = 2mm

So spacing from lens mount face to camera mounting face = 19.5mm (if I've got the filter correction right).

[Gina]

Been working on the design of a framework for the 200mm lenses in SketchUp.  Here's a couple of screenshots.

Lens and adapter plates

Some of the plastic framework added

More framework will be added for rigidity and to enclose the filter section.  The filter will be on a removeable slide which will fit between the two plastic parts on the camera end with foam rubber or plastic to provide a light seal.

[Gina]

Been looking into producing threads in SketchUp but no joy so far.  I could use a standard adapter to convert Pentax/Praktica 42mmx1mm thread to Canon EF bayonet (I have several) and use a printed bayonet connection.  But then there's the 42x0.75 T2 thread to connect to the camera.  Not sure that printed threads so fine would be practical anyway.  Think I'll stick with my original plan of using adapters or turning the part in the lathe.  The latter would produce the nicest results I think.  It's only the lens to camera connection that's really critical, all the rest can be printed in plastic.

[Horwig]

I know you already have lenses Gina, but it might be worth your while to consider buying a set of Pentax 67 lenses off Ebay, or Ffordes. Very reasonable prices, excellent lenses, and more importantly, stupidly long back focus, more than enough to put filters and other toys.

http://www.ffordes.com/product/14072217072631

http://www.ebay.co.uk/itm/Pentax-67-Super-Takumar-200mm-f-4-telephoto-lens-/141377097439?pt=UK_Lenses_Filters_Lenses&hash=item20eabb4edf

You can buy a Pentax 67 adaptor to whatever for about 18 or 19 quid off ebay, and mod it to mount onto a panel.

http://www.ebay.co.uk/itm/Pentax-67-Lens-to-Canon-EOS-Mount-Camera-Adapter-Ring-/120563288260?pt=UK_Photography_CameraLenses_Lens_caps_hoods_adaptors_ET&hash=item1c1221c8c4

This is what I did with an adptor to fit it onto my sx system.

Worth a think?

Huw

[Gina]

Thank you Huw   I guess there's no reason why 6x7 lenses should not be used - there should be plenty of spare resolution   Good thought.  Might be able to fill a gap in my range that way

[Gina]

Looks like I should be getting a second 460EX in the next few weeks and another SMC Takumar 200mm f4 lens even sooner so I should be having two top end imaging systems soon.  I could add a 135mm SMC and 314L+ for the third.

[Gina]

I'm considering a totally different mounting system for the new triple imaging rig.  In the earlier version I provided rotation for each camera at the point where the camera was mounted onto the framework.  In the new version I shall have the lens, filter and camera as one unit including the lens focussing system.  Then I'm thinking of fitting each imaging unit into a turret with facility to rotate. 

Individual units will be aligned by preset rotation adjusters within the turret if this is found to be needed.  With the lens to camera connection being fixed and basically cylindrical I shall probably clamp this part into the framework that contalns the focussing parts and which then fits into the turret.  This will enable the camera to be aligned with the framework by sight.

I need to think a lot about how I can make such a large thing like the turret.  I need to work out dimensions.  Then consider whether to mount the guide lens and camera in the middle or completely separately outside the turret.

[Gina]

I've also been thinking about filter mounting.  Since I can only use a 460EX on one optical system at a time I shall have to take one off the tripple imaging rig when I want to use one of the telescopes.  That will leave the optical path open so the filter could be fitted inside with access through the camera mounting.  Unless I were to buy another set of Astrodon NB filters (cost ) I will have to swap the current set from one rig to the other.  Unscrewing three cameras to use filters is not much worse than unscrewing one to use the camera   So I could probably arrange a screw filter mounting inside the tube from lens to camera.

[Gina]

Back to the overall construction, I think a turned aluminium part to connect lens to camera will be the best option though I shall need to learn how to cut threads on the lathe.  This would then be black anodised.  However, to test out the measurements and get that right I plan to produce the part in ABS plastic on the 3D printer.  The printed part would not have printed threads but be a fairly tight fit onto/into the threads of the optical parts and self-thread as the metal parts are fitted.  (I did this with the all-sky camera lens.)

[Gina]

Goodness me, there's certainly a lot to think about with this project and expensive   Hope it'll be worth it   Oh, I'm sure it will   I need difficult things to get my teeth into

[Gina]

Amazingly one segment of the turret just fitted onto the print bed of the UP printer   This forms a third of a spur gear that will be used to rotate the turret.  I think I might go for rather larger teeth though.  Each imaging unit will be in the form of a segment of a cylinder with the three fastened together.

[Gina]

Some further progress on this project.  Printed some more parts.  These are for the SMC Takumar 200mm lenses, supported by the adapter tube to the camera (460EX mono) and the lens hood.  The inbetween plate carries the stepper motor focussing system driving the focus sleeve by timing belt.  This is one segment of three, of the turret, which will be carried by spur gears on shafts, permitting the whole rig to be turned to get the best framing of DSOs.

[Horwig]

Impressive!

H